Th nature of cell surface interations which allow the mononucleate myoblasts to recognize each other, aggregate, and finally fuse to form multinucleated myotubes will be examined. In particular a role of lectin-carbohydrate interactions as applied to the previously described, B-D-galactoside specific and developmentally regulated lectin of embryonic chick muscle will be investigated. To this end 1) surface labelling technique will be applied to intact myoblasts; the resulting labelling patterns will be examined by SDS-PAGE followed by autoradiography to verify that this lectin is indeed located on the cell surface. 2) The existence of specific lectin receptors will be examined by studying of the binding of 125I-labelled muscle lectin to electrophoretograms and to intact myoblasts at different stages of differentiation. Isolation of these receptors by gel filtration in the presence of detergents is anticipated. 3) Rabbit antisera to the lectin, which are being prepared at present, will be purified and fragmented. The resulting Fab fragments should inhibit myoblast fusion if lectin-carbohydrate interactions are indeed involved in myoblast differentiation.